1. Field of the Invention
The present invention relates to a technique for diagnosing rechargeable batteries capable of repeatedly undergoing discharging/recharging cycles. The present invention also relates to a technique for collecting information useful to diagnose rechargeable batteries.
2. Description of the Related Art
A variety of cordless electrical devices, such as mobile telephones, notebook computers, cordless vacuum cleaners, and cordless power tools, etc., utilize rechargeable batteries as their power source. In a case where a cordless electrical equipment malfunctions, it is necessary to know if the fault lies with the electrical equipment or with the rechargeable battery.
Furthermore, in a case where industrial goods, such as automobiles or computers, are manufactured on a mass production line by a power tool powered by a rechargeable battery, it may be possible that the tightening torque of the power tool is insufficient or an assigned operation cannot be completed within an allotted time frame, if a deteriorated rechargeable battery is used. Accordingly, it is necessary to determine when battery degradation has progressed beyond a permissible level.
The internal resistance of a rechargeable battery increases abruptly as degradation progresses. Japanese Laid-Open Patent Publication No. 2000-223164 discloses a device that measures the internal resistance of a battery and compares the measured resistance with a reference value to determine whether the degradation has progressed.
The charging/discharging capacity of rechargeable batteries also decreases abruptly as the degradation of the batteries progresses. Japanese Laid-Open Patent Publication No. H11-233162 discloses a device that measures the charging/discharging capacity of a battery and compares the measured capacity with a reference value to diagnose whether degradation has progressed.
A charging device capable of counting a number of charging operations of a rechargeable battery is known. When a battery that has already been charged a prescribed number of times is set to the charging device for recharging, this information is transmitted to an operator, thus informing the operator that battery degradation has progressed. A same charging device may charge two or more batteries. Japanese Laid-Open Patent Publication No. H10-66266 discloses a technique wherein batteries are provided with an ID respectively and the number of charging operations for each battery is counted with reference to the battery ID.